The heaviest mirrors are plate glass in solid wood frames. Almost all heavy mirrors are mounted in frames. Mounting one on a wall requires using picture wire and small nails pounded into the back of the frame. Mirrors without frames require the use of an adhesive and mounting brackets. Positioning either type of mirror should be done adjacent to the wall studs for additional support. Use an assistant when installing a heavy mirror to avoid potential damage from dropping it.
Locate the studs in the wall using a stud finder. Follow the directions included with the stud finder for proper operation. Mark the position of the studs with a pencil.
Mark an "X" at the base of each stud where you want the bottom of the mirror to sit. Draw a straight, level line across the wall, using a level as a straightedge to indicate where the bottom of the mirror will sit.
Install a mounting bracket along the line made in Step 2 for each stud. Mirror mounting brackets are flat boxes that mount to the wall with a wood screw that is included with the bracket. A J-shaped piece of metal slides into the box to create a groove that holds the mirror. Drive the wood screw through the hole in the bracket into the stud with a drill, so that the bottom of the bracket is flush with the line made in Step 2. Mount one bracket for each stud. Insert the J-shaped metal into each bracket so that the groove points up.
Set the mirror onto the brackets and hold it against the wall. Mark the top of the mirror on the wall.
Install one mounting bracket per stud along the line made in Step 4. Do not install the J-shaped metal into the brackets.
Spread mirror adhesive across the back of the mirror in a "S" pattern so that the adhesive looks like a snake across the back of the mirror.
Set the mirror into the grooves for the lower brackets and press the mirror against the wall. Slide the J-shaped metal pieces into the brackets on top so that the groove faces down and grabs the mirror. The metal pieces will click as you insert them into the brackets.
Heavy mirrors with frames are easy to install. Tap a small nail into the left and right side of the back of the frame for the mirror. Leave a small amount of the nail exposed. Wrap picture-hanging wire around one nail and stretch it across to the other nail. Wrap the wire around the other nail. Hang the mirror like a picture, but centre the mirror over a wall stud for added stability.